Proper context attribute for a hotkey to toggle mesh display overlays?
The mesh is the data part of the active object hence,

active_object.data.show_edge_crease


or perhaps since it is the edit object:

edit_object.data.show_edge_crease




Sliding down the info area header at the top to reveal the messages gives you the context paths.

As for part ii) of your question adding an "add shortcut" menu, sounds like a good idea.  This can be "hacked" by overriding say the edit translations operator in the menu.